So lets say for argument sake, that we've got River "bundles" that are annotated with package imports (dependencies) and exports.
Using Bharath's proposed 3 bundle nomenclature for services... Lets say that a third party services defines a service api in a bundle. Service api must only change in a backward compatible manner. A client imports the service api packages. A service proxy imports the service api packages. The service api classes are already loaded in the client jvm because the client imported them. The service proxy is deserialised in the client jvm. Before the proxy can be deserialized the RMIClassLoader must first determine whether the proxy's bundle (exact version) exists, if not it needs to request OSGi to provision & load that bundle. When the proxy bundle is loaded, it imports the same service api packages visible to the client. But how do we ensure we have a compatible service api in the client jvm? Because the lookup service finds matching interfaces. When those service api interfaces were marshalled as arguments to the lookup service by the client, they were matched on serial form, so the client will only ever receive compatible results. Regards, Peter. Sent from my Samsung device. Include original message ---- Original message ---- From: "Michał Kłeczek (XPro Sp. z o. o.)" <michal.klec...@xpro.biz> Sent: 26/01/2017 08:30:58 am To: dev@river.apache.org Subject: Re: OSGi I haven't been aware of ObjectSpace Voyager. I just briefly looked at it and it seems like it is based on Java 1.x (ancient beast) and - as I understand it - the issues you describe are mainly caused by having only a single class name space (single ClassLoader). But sending IMHO class bytes in-band is not necessary (nor good). What is needed is: 1. Encoding dependency information in codebases (either in-band or by providing a downloadable descriptor) so that it is possible to recreate proper ClassLoader structure (hierarchy or rather graph - see below) on the client. 2. Provide non-hierarchical class loading to support arbitrary object graph deserialization (otherwise there is a problem with "diamond shaped" object graphs). A separate issue is with the definition of codebase identity. I guess originally Jini designers wanted to avoid this issue and left it undefined... but it is unavoidable :) Thanks, Michal Gregg Wonderly wrote: > That’s what I was suggesting. The code works, but only if you put the >required classes into codebases or class paths. It’s not a problem with >mobile code, it’s a problem with resolution of objects in mobile code >references. That’s why I mentioned ObjectSpace Voyager. It automatically >sent/sends class definitions with object graphs to the remote VM. > > Gregg > >> On Jan 23, 2017, at 3:03 PM, Michał Kłeczek (XPro Sp. z o. >>o.)<michal.klec...@xpro.biz> wrote: >> >> The problem is that we only support (smart) proxies that reference only >>objects of classes from their own code base. >> We do not support cases when a (smart) proxy wraps a (smart) proxy of >>another service (annotated with different codebase). >> >> This precludes several scenarios such as for example "dynamic exporters" - >>exporters that are actually smart proxies. >> >> Thanks, >> Michal >> >>
